1. Field of the Invention
Embodiments described herein relate generally to a charged particle beam writing apparatus and a charged particle beam writing method and, for example, to a writing apparatus that writes a pattern on a substrate on which a substrate cover is mounted by using an electronic beam and a method therefor.
2. Related Art
Lithography technology taking charge of development of increasingly finer semiconductor devices is an extremely important process that, among semiconductor fabrication processes, solely generates a pattern. In recent years, with increasing integration of LSI, the circuit linewidth required for semiconductor devices becomes ever finer year after year. To form a desired circuit pattern for such semiconductor devices, a high-accuracy original picture pattern (also called a reticle or mask) is needed. Electron beam (EB) writing technology has intrinsically excellent resolving power and is used for production of a high-accuracy original picture pattern.
FIG. 16 is a conceptual diagram illustrating the operation of a variable-shaped electron beam writing apparatus. The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a rectangular opening 411 formed to shape an electron beam 330. A second aperture plate 420 has a variable-shaped opening 421 formed to shape the electron beam. 330 having passed through the opening 411 of the first aperture plate 410 to a desired rectangular shape. The electron beam 330 having been irradiated from a charged particle source 430 and passed through the opening 411 of the first aperture plate 410 is deflected by a deflector and passes through a portion of the variable-shaped opening 421 of the second aperture plate 420 before being shone on a target object 340 mounted on a stage continuously moving in a predetermined direction (for example, the X direction). That is, a rectangular shape capable of passing through the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a writing region of the target object 340 mounted on the stage continuously moving in the X direction. The method of creating any shape by allowing an electron beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is called a variable shaping method.
When a pattern is written by a writing apparatus, an outer circumferential portion of a target object may be covered with a frame-shaped mask cover so that an insulated portion on the end face of a mask (substrate) to be the target object is not charged with reflected electrons of an irradiated electron beam. In such a case, the mask cover is stored on a transport path in a vacuum inside the writing apparatus to be mounted on a mask when a pattern is written. Misregistration (error) may arise between the mask and mask cover. If the mask cover is used for writing a pattern a plurality of times without performing alignment, errors are accumulated and misregistration that cannot be tolerated may arise. Thus, to prevent such errors from being accumulated, it is desirable to mount the cover in an accurate position with respect to the mask by performing alignment each time before the cover is mounted on the mask. Thus, performing alignment of the mask cover after the mask cover being removed from the mask by separately providing a fulcrum for supporting the mask cover and a fulcrum for alignment of the mask cover is proposed (see Published Unexamined Japanese Patent Application No. 2011-14630, for example).
In addition to misregistration between the mask and mask cover, misregistration from the ideal position of the mask during transport is assumed. To address such a problem, alignment of the mask has been performed on the transport path. To find the position of the mask, an image of a region containing corners of the mask captured by a CCD camera or the like from above or below has been used. However, illumination toward the camera across the mask is needed to capture an image by the camera and diffraction conditions of illumination change from mask to mask to be measured due to the end face shape of the mask substrate, the C surface shape of mask corners, and variations of transmittance. Thus, measured results vary. Further, the measuring time is long due to operations to turn on and turn off a lighting system.
As described above, it is desirable to suppress misregistration between a mask substrate and a mask substrate cover. It is also necessary to measure the position with high accuracy to find the amount of misregistration. However, the method for solving these problems adequately has not been established.